1. Field of the Invention
This invention relates to a front side member, a side sill and other structural members of an automobile provided with a rigid portion formed in a closed cross section by an inner panel and an outer panel.
In the structural members of the automobile, there are a front side member 22 and a rocker, that is, a side sill 24 which extend in the longitudinal direction of a car body 20, and, in addition, a cowl 26 located between the front side member 22 and the side sill 24 and extending in the lateral direction of the car body 20 as shown in FIG. 13. The present invention, however, relates to a structural member extending in the longitudinal direction of the car body.
2. Description of the Prior Art
As shown in FIGS. 14 and 15, the front side member 22 is provided with a rigid portion 32 formed in a closed cross section by an inner panel 28 and an outer panel 30 and extending in the longitudinal direction of the car body, and a base portion 34 extending inwardly and downwardly in the lateral direction of the car body from the rigid portion 32 (refer to Japanese Utility Model Public Disclosure (KOKAI) No. 3-16580). A reinforcement 36 having a cross section providing a so-called "hat shape" is provided in the closed cross section to enhance the rigidity of the rigid portion 32.
Since the base portion 34 extends from the rigid portion 32 into the car body inwardly in a front view thereof as shown in FIG. 16, the rigid portion 32 is vibrated between the upper inside and the lower outside in the car body as indicated by an arrow A when any vertical vibrations are applied to the car body during running of the automobile.
On the other hand, the closed cross section of the rigid portion 32 of the front side member is substantially symmetrical with respect to a horizontal plane thereof as shown in FIG. 15. Therefore, rectangular coordinate axes I.sub.1 and I.sub.2 as principal axes of the closed cross section are set as illustrated. Namely, the axis I.sub.1 is horizontally located at the center of the closed cross section, and the axis I.sub.2 is located perpendicular to the axis I.sub.1. Herein, in the axis I.sub.1, a moment of inertia with respect to the axis I.sub.1 is maximized, and in the axis I.sub.2, a moment of inertia with respect to the axis I.sub.2 is minimized.
Since the rigid portion of the front side member is vibrated between the upper inside and the lower outside of the car body at the time of running of the automobile, and in the rectangular coordinate axes as principal axes of the closed cross section in the rigid portion, the axis I.sub.2 is perpendicularly located so that the rigidity in the lateral direction is reduced. The rigid portion may sometimes resonate with the vibration at a relatively low frequency, e.g., the vibration of a suspension system at 20 to 30 Hz.
The structure of the side portion in the car body is provided with the side sill 24, a roof side rail 40 extending in the longitudinal direction of the car body and arranged upwards at an interval from the side sill 24, further, a front pillar 42, a center pillar 44 and a quarter panel 46, and the structure is integrally formed from these members, as shown in FIG. 19. The side sill 24 is formed so as to present a closed cross section by an inner panel 48 and an outer panel 50, as shown in FIG. 17 (refer to Japanese Utility Model Public Disclosure (KOKAI) No. 60-51183).
Since the shape of the side sill 24, in particular, that of the outer panel 50 appears itself on the outside, the shape is decided with a view of satisfying any demands with respect to a design and easily connecting to the center pillar 44, while a rigidly thereof is taken into consideration. However, the rigidity is not determined in consideration of the directions of two rectangular coordinate axes as principal axes of the closed cross section in the side sill 24 in connection with other members.
In the two rectangular coordinate axes I.sub.1 and I.sub.2 which become principal axes of the closed cross section in the side sill 24, the axis I.sub.1 extending in the direction of minimizing a moment of inertia is directing to the inside and upside of the car body as shown in FIG. 17. Therefore, the side sill 24 is easily transformed in the direction of the axis I.sub.1. When the car body is vibrated in a vertical direction, vibrational component f in a left or right direction arises in the side sill 24 to thereby vibrate the center pillar 44 in the left or right direction.
When the center pillar 44 is vibrated in a left or right direction, a leftward or rightward vibration is induced at the upside portion of the car body and the booming noise in the compartment of the car is enlarged. In addition, the distribution of moment M of the center pillar by an external force F applied on the side sill 24 becomes as shown in FIG. 18, and since a large torsional moment is generated in the roof side rail 40, the resulting apparent rigidity of the car body is lowered.